Surface treated steel for the use of forming operation

ABSTRACT

SURFACE TREATED STEEL SHEET FOR USE IN A FORMING OPERATION HAVING A COATING LAYER OF A COMPOSITION, WHICH IS SOLID AT AMBIENT TEMPERATURE, COMPRISING 95-60 WEIGHT PERCENT OF A LUBRICANT COMPONENT CONSISTING OF 90-60 MOL PERCENT OF A HIGHER FATTY ACID AND 10-40 MOL PERCENT OF AN AMINE, AND 5-40 WEIGHT PERCENT OF A COUPLING AGENT, ON THE SURFACE OF THE STEEL SHEET.

United States Patent O US. Cl. 117-134 4 Claims ABSTRACT OF THE DISCLOSURE Surface treated steel sheet for use in a forming operation having a coating layer of a composition, which is solid at ambient temperature, comprising 95-60 Weight percent of a lubricant component consisting of 90-60 mol percent of a higher fatty acid and 10-40 mol percent of an amine, and 5-40 weight percent of a coupling agent, on the surface of the steel sheet.

This invention relates to a surface treated steel sheet use in a forming operation having a preliminary lubricant film comprising a fatty acid, an amine and a plasticizer on the surface of the steel sheet.

A lubricant is generally required to diminish the friction and to prevent the formation of burning and press defects when a steel sheet is subjected to a forming operation such as press forming. As lubricant for this purpose, liquid types, such as, oily products, and emulsion type have hitherto been used. Recently, attempts have been made to apply a solid lubricant film preliminary on the steel sheet surface in order to improve the lubricity as well as the workability. At present a metallic soap based lubricant and a plastic film are used for such a preliminary lubricant. While a metallic soap based lubricant forms a solid film having an excellent lubricating ability, it has certain disadvantages. Thus, as it is applied in the form of an aqueous solution, in forming the film, prolonged high temperature heating is required to dry the coating. This requires a large production facility, and increases the production cost. Also, the heating accelerates aging the steel sheet, substrate, thereby deteriorating the steel quality. On the other hand, a plastic film has an excellent lubricity, after forming it is difiicult and expensive to make.

The present inventors have recently discovered, as a consequence of various investigations on this problem, that a steel sheet having a coating film, which is solid at ambient temperature, comprising a higher fatty acid with a suitable amount of an amine as a main constituent, can eliminate the problem in manufacturing encountered by using a steel sheet coated with said metallic soap based lubricant or with said plastic.

According to the experiments on the industrialization of this method by the present inventors, this preliminary lubricant film has many advantages such that the film has an excellent lubricating ability, even when only a small amount is used, comparable to that of the commercial high grade press oil, such that the film has an excellent rust preventing ability and is easily removed, morover, the film can be applied on the steel sheet surface with simple equipment. On the other hand, however, it was found that said preliminary lubricant is squeezed out and deposits as a white powder on the surface of the forming die in the press work, thereby making inferior goods and decreasing the productivity.

The present inventors investigated the reason for the deposition of the white powder, and found that the powdery white crystals are formed when the composition comprising a higher fatty acid and an amine is cooled in the presence of water (including water vapour). This is because the fatty acid and its amine salt are insoluble in water.

In order to prevent the squeeze out of white powder, water on the steel sheet surface must be removed as completely as possible before coating, and no water should be allowed to adhere, after coating. For this reason, the coated steel sheet should not be cooled in open air. In these instances, however, there are problems, such as sufficient drying is necessary before coating, and the handling of the steel sheet after coating is troublesome. For instance, when the steel sheet after coating is kept below 15 C., water vapour in the air condenses and the white powder is easily squeezed out. Also, a severe packing is needed when keeping the product in a moist environment.

We attempted to solve this problem by adding a suitable reagent and found that the addition of a plasticizer having both hydrophilic and lipophilic radicals (for instance, a coupling agent having a oxyethylene radical) as a coupling agent is quite effective. The action of the coupling agent is to disperse water uniformly in the lubricant film comprizing a fatty acid and an amine, and to give plasticity to the film obtained, thus preventing the deposition of white powder in the film as well as the adhesion and accumulation thereof on the surface of the die during the press forming.

This invention is performed on the basis of above-mentioned knowledge. The essential point of the invention is a surface treated steel sheet having a coated layer of a composition, soild at ambient temperature, comprising 95-60 weight percent of a composition consisting of 60 mol percent of a higher fatty acid and 10-40 mol percent of an amine, and 5-40 weight percent of a coupling agent having both hydrophilic and lipophilic radicals, particularly the oxyethylene or oxypropylene radical, on the surface of the steel sheet. Said steel sheet possesses excellent properties for the use in a forming operation. The lubricant film in this invention is considered to of a salt formed by the reaction between a higher fatty acid and an amine, free higher fatty acid remaining unreacted in excess, and a coupling agent.

The lubricating action in the steel sheet of this invention may be due to the following reasons. Namely, in the range where the interface pressure is low, the coating layer itself has a fluid lubricating action, the layer acting as a very viscous fluid; and, on the other hand, when the contact pressure becomes high, the metallic soap, which is formed on the surface of the steel sheet by the reaction between the surface part of the steel sheet and free higher fatty acid, acts as a boundary film, decreasing the friction. Particularly, differing from the case when a metallic soap is applied on the surface of steel sheet, the metallic soap, which is formed between the surface of steel sheet substrate and higher fatty acid as above-mentioned, orientates regularly and is combined firmly on the surface of the steel sheet substrate, and consequently possesses excellent properties as a boundary film. It is considered further that, even when a part of the boundary film is broken due to a high contact pressure, free fatty acid in the film remaining in excess repairs the boundary film at once. For these reasons, an excellent lubricating eifect can be obtained with only a very thin coating.

Steel sheet substrates for this invention are, for example, hot rolled medium plate, hot rolled thin sheet, cold rolled steel sheet, blue sheet and various kinds of plated steel sheet. They will be called in a general term simply as steel sheet hereinafter.

Higher fatty acid in this invention means fatty acid whose carbon number is more than 10. Among them, those solid at ambient temperature and used in this invention include, for instance, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid and arachic acid. A mixture of these fatty acids is also included. Those containing a mixture of these fatty acids and corresponding unsaturated fatty acids as a main constituent, such as tallow fatty acid, hydrogenated fatty acid, hydrogenated castor oil fatty acid and naphthenic acid, may also be applied. While said higher fatty acids are usually obtained commercially as a mixture, they belong naturally within the scope of the object of this invention.

Amines used in this invention include, for instance, primary amines such as octylamine and cyclohexylamine, secondary amines such as diisopropylamine and dicyclohexylamine, tertiary amines such as triethylamine and triethanolamine, oxazines, imidazoles, and mixtures thereof.

The coupling agent used in this invention means a plasticizer having both hydrophilic and lipophilic radicals, particularly the oxyethylene radical, -CH CH O, or oxypropylene radical, CH CH CH O-, in its molecule and whose hydrophile-lipophile balance value, (HLB- value),

amount of hydrophile radical I99 amount of hydrophile radical +amount of lipophile radical HLB value:

where R: C -C3 and m: 1-20. Polyoxyethylene alkylphenolether,

where R:C -C and m: 1-10,

Phosphoric acid ester and the diester of polyoxyethyh ene alkylphenolether,

l5, and mixtures thereof. In the case of phosphoric acid ester, its amine salt and alkali salt are also effective.

and

Now, the reason why the mixing ratio of each of the components is limited in the preliminary lubricant used for the steel sheet of this invention will be explained.

In the composition used in this invention, the higher fatty acid takes charge of the lubricating action in the forming operation, and its effect differs depending on the mixing ratio with the amine. On the other hand, the amine is added for the purpose of improving the rust preventing ability, easiness for degreasing and the ease of coating. In the composition consisting of a higher fatty acid and amine, when the content of the amine is less than 10 mol percent, the effect of the coating him in improving the rust preventing ability is insufiicient, and the ease degreasing (or removing) the film is also insufficient, thus requiring a long period for degreasing. On the other hand, when the content of the amine exceeds 40 mol percent, the rust preventing ability in a high moisture condition becomes minimal; and as the content of the higher fatty acid becomes correspondingly small, the lubricating ability is insufiicient.

As for the ease of the composition in this invention for coating steel sheet, if the higher fatty acid and amine is used in a nearly equal mol ratio (fatty acidzamine =2/3-3/2), a salt is formed easily by the reaction between them, elevating the melting point of the composition remarkably (for instance, the melting point of an equimolar mixture of stearic acid and cyclohexylamine is about C.). Consequently coating the steel sheet at ambient temperature is difiicult, and it is necessary to first heat the steel sheet before coating. To heat steel sheet for this purpose requires a large installation, and moreover the heating accelerates aging of the steel sheet, thus deteriorating the steel quality. On the other hand, from the reason as above stated that free higher fatty acid possess an excellent boundary lubricating ability when press forming is carried out under a severe condition at a high contact pressure, the existence of free higher fatty acid in the coating film is necessary.

The coupling agent is added for the purpose of preventing the deposition of white powder in the film in both cases when the lubricant film is applied on the surface of steel sheet on which a trace of water is remaining, and when the steel sheet coated with a lubricating film is stored at lower temperatures. Plasticizers having both hydrophilic and lipophilic properties are most excellent for the coupling agent. When the content of the coupling agent is smaller than 5% in Weight, the prevention of said deposition is not observed; and when the content exceeds 40% in weight, the composition is not a solid at ambient temperature as said coupling agents are liquid at ambient temperature, and the characteristic in lubricity of solid substance at ambient temperature and one of the features of this invention is lost. Therefore, the content of the coupling agent is desirously 540% in weight.

In this invention, While it is adequate that the steel sheet is coated previously with said preliminary lubricant and is used as a preliminary lubricanttreated steel sheet, the preliminary lubricant may also be applied on the surface of the blank or forming die just before pressing as in the case of common press Working oil.

As for the coating method of the steel sheet with said preliminary lubricant, for example, the composition may be made molten by heating and applied by means of a roll coater and the like, or the composition is dissolved in an organic solvent and the liquid so obtained is applied by roller coating, spray coating, electrostatic coating, brush coating or flow coating. When a small quantity of an organic solvent is added to control the melting point in the hot melt coating, the coating operation becomes much easier. The solid composition of this invention may also be applied directly as fine particles to adhere on the surface of the steel sheet by spraying etc., and then made molten by heating with, for instance, the use of an infrared beam, hot air or heating roller to form a uniform coating film.

The composition of this invention is effective even when the amount coated is very smallffoninstance' about 0.1

g./m. and the lubricity increases with the increase of the coating amount. However, fromthe point of blocking, slipping at the roller in using the-coated steel sheet as well as the period necessary for the removal of the film and the pollution of the remover liquid in the final removal of the coating film, the practical upper limit of the coating amount is g./m.

Various advantages of steel sheet prepared according to this invention are set forth below:

(1) Due to the excellent lubricity of the coating layer, application of additional working oil is not necessary in the pressing operation. For this reason, the productive efficiency is remarkably improved. The yield ratio of the pressing operation is also very high.

(2) Even if water is adhered on the surface of the steel sheet or the product is stored at a low temperature place for a long period after the treatment, almost no aging of the coating film (squeeze out of white powdery substance) takes place; and consequently no deposition of the film composition occurs on the forming die during the pressing operation. There is no problem with cleaning the die due to the deposition of preliminary lubricant during the pressing operation, and the working efiiciency is increased.

. (3) Since the'coating' layer is'solid, not sticky and its filmis thin, the coating film is not destroyed when the steel sheets are piled, the blocking does not occur and dust scarcelysticks on the product.

(4) Welding, such as spotand seam welding, of the steel sheet is possible without degreasing after the forming operation. Adhesion of the sheets by means of an adhesive is also possible.

(5) The coating film can easily be removed by an alkaline degreaser or an organic solvent. As the coating amount is small, pollution of the degreaser liquid is minimal.

(6) As an amine is added to the higher fatty acid, the rust preventing ability becomes greater. The steel sheet of this invention shows, with only a small amount of the coating material, for instance with an amount of 0.1 g./m. a rust preventing property equal to or more than the same property the steel sheet coated with a common rust preventing oil. There is no need for coating with an additional rust preventing oil in transporting the steel sheet of this invention, and the rust preventing ability after press-forming is also excellent.

(7) Even when a coating method accompanying drying is adopted in this invention, it is sufficient'to dry at low temperature for a short period. Therefore, it requires only a simple and small equipment, and there is no deterioration of the steel sheet substrate by the coating operation.

EXAMPLE 1 Various coating materials relating to this invention as shown in Table 1 were applied on cold rolled rimmed steel sheet with a thickness of 0.8 mm., and their lubricating ability, rust preventing ability and easiness of removing of the coating film were tested. Samples No. 1-8 differ in the mixing ratio of fatty acid and amine, including the compositions without the scope of this invention, samples No. 9-16 show the effect of various kinds of fatty acid under the addition of definite amounts of amine and coupling agent. As a comparison, commercial rust preventing oils (No. 17-18) and commercial mineral press oil (No. 19-20) were also tested. The results were as shown in Table 2.

As it is obvious from Table 2, when the lubricating ability is compared with that of common press oil, fatty acids having a carbon number of more than 10 (caprie acid and fatty acids having a carbon number more than that of capric acid) are advantageous. Namely compositions which are solid at ambient temperature sh'oW excellent lubricity. Among them, palmitic acid, stearic acid and a mixture of these show particularly excellent effects. As for the ratio of fatty acid and amine, it is adequate that the amount of fatty acid is more than the stoichiometrical equivalent.

I From the standpoint of the easiness of removing the coating film, when the content of amine in the lubricant component becomes lower than 10 mol percent or exceeds 40 mol percent, a relatively long period is needed for its removal.

As for the rust preventing ability, when the content of amine in the lubricant component is less than 10 mol percent, the rust preventing ability in open air is insufficient, and when said content exceeds 40 mol percent, the rust preventing ability in moist atmosphere becomes insufficient.

Judging from the results of these experiments collectively, it is advantageous that the ratio of fatty acid and amine in the lubricant component is: fatty acid 90-60 mol percent and amine 10-40 mol percent.

TABLE 1 Lubricant component Mol M01 Weight Coupling Weight Titer, No. Fatty acid percent Amine percent percent agent percent C 100 DCHA 0 90 AP 20 65 95 DCHA 5 80 AP 20 60 90 DCHA 10 80 AP 20 57 80 DCHA 20 80 AP 20 53 70 DCHA 80 AP 20 50 60 DCHA 80 AP 20 59 DCHA 50 80 AP 20 86 25 DCHA 75 80 AP 20 24 9 Caprylic acid 80 OHA 20 70 PEG 30 10 10. Oapric acid 80 CHA 20 70 PEG 30 20 11 Laurie aeid 80 CHA 20 70 PEG 30 27 12.... Myn'stic aeid 80 CHA 20 70 PEG 30 41 13 Palmitic acid 80 CHA 20 70 PEG 30 46 14 Stearic acid 80 CHA 20 70 PEG 30 15.- rtlrlcmhicc acitlld CHA 20 70 PEG 30 66 e 10 ac 16 geld" }DCHA 2o 70 PEG so 45 17 Commercial rust preventing oil A Viscosity, SUS 42 seconds. 18 Commercial rust preventing oil B Viscosity, SUS seconds;

19 Commercial press oil (mineral oil) A Viscosity, SUB seconds. 20 Commercial press oil (mineral oil) B Viscosity, SUS 2,000 seconds.

N ore-D CHA dlcyclohexylamine; CHA= cyelohexylamine; AP nouylphenoxy-polyoxyethylene phosphoric acid ester; PE G =polyetliy1eneglycol.

TABLE 2 Lubricity Maximum 7 punch load Rust preventing ability Conical in cylin- Coating Erickson cup rical cup Time for In package amount, value, value, drawing, degreasing, Ininstrucontaining gJm." mm. mm. ton second mentscreen moisture 0.5 11.0 37.3 2.70 50 XX X 0.5 11.7 37.2 2.67 30 X A 0.5 12.1 37.0 2.61 10 A 0.5 12.0 35.9 2.57 A 0.5 12.0 35.9 2.55 5 0 0.5 11.9 37.1 2.52 5 0 0 0.5 11.5 37.4 2.66 so A X 0.5 10.9 38.1 2.85 30 X X 0.5 10.8 38.0 2.86 5 x a 0.5 11.5 37.3 2.75 5 A 0 0.5 11.6 37.1 2.73 5 0 0 0.5 11.9 37.1 2.73 5 0 0 0.5 12.1 36.8 2.62 5 0 0.5 12.1 35.9 2.50 0 0 0.5 11.8 37.2 2.69 0' 0 0.5 12.2 35.4 2.57 5 o 5 10.8 37.3 2.85 30 A XX 8 11.4. 37.1 2.55 120 0 X Composition of the degreaser bath was: G./l.

e o ubri 1 Testma thods y v V NaOH 10 (i) Ericksen test. Only the punch side of blank was Na PO -12H O 10 treated. The Ericksen value is obtained from a test where- Surface active agent (octylphenol polyoxyethylene-. in a lubricated test piece is placed in a die and a punch ether) 0.5 presses the test piece into the die. The Erickson value is 3, Testin methods of rust revenfin abilit represented by the distance in millimeters traveled by p y the punch until a crack reaching the back surface of the Test 111 lnSmlmelft A g leaf treated t st piece occurs in at least one place in the test piece. steel sheet was stored in an instrument screen for 30 The Ericksen test is described in Sheet Metal Industries, 5 Y

(ii) Conical cup test. Only the die side of blank was treated. The conical cup value is obtained from a test wherein a. lubricated test pieceis placed in a conical die. A punch presses the test piece into the die, thus shaping the test piece into a conical cup. At the point where the bottom of the cup has at least a 0.05 mm. break, the maximum and minimum outerydiameters of the upper edge of the conical cup are determined. The conical cup value is the arithmeticalmean of the maximum and minimum outer diameters expressed in millimeters. The conical cup test is described in Sheet Metal Industries, 44, 21 (1967).

(iii) Cylindrical cup drawing test. Both sides were treated. In the cylindrical cup drawing test, circular blanks 80 mm. in diameter and lubricated on both sides are drawn by a fiat bottomed punch 40 mm. in diameter. The maximum punch load is measured. The smaller the value, the better the lubricity. The test is described in Sheet Metal Industries, 40, 620 (1963).

(2) Coating film removing test I Immersed in a degreaser bath (at 50 C.) fitted with a stirrer, and the period necessary for degreasing, judging from the'water repellency, was measured.

' (ii) Test in package containing moisture. The treated steel sheets were piled, a filter paper soaked with water being inserted anywhere between the sheets, packed and stored at 37 C. for 30 days. Thus the condition was severer than in the case of common packing. The result in Table 2 was a collective result in which the steel sheet was in contact with a filter paper soaked with water or not.

(iii) Expression of the degree of rust formation:

A cold rolled steel sheet was degreased, washed with water, dried, coatedwith a composition with different mixing ratio of the lubricant component and the coupling agent, audstor'ed in a room at 10 C. for 2 weeks. The surface condition was observed, and the accumulation of coating composition on the'pressing die was investigated in pressing the sheet-to obtain an outer part of an automobileffor riding; The results were as shown in Table 3.

TABLE 3 Coating film composition Lubricant Coupling component, agent, wt. percent wt. percent Surface condition Deposition of the composition on the die during press work 100 0 X Scattered deposition of white crystals. Die should be cleaned after pressing 5-10 pieces. 7

99 1 A Scattered white spots are observed Die should be cleaned after pressing 10-20 pieces. 5 0 Smooth with no squeeze out; 90 10 N0 deposition takes place even when 100 pieces are pressed 80 20 d0 ti 1 7o 30 con nuous y. 1 e0 40 do.; r 7 V 50 50 The surface s fluid Although no desposition, the lubricating eflect is small.

9 Stearie acid- White crystals on total sunace Frequent cleaning is needed as the deposition on the die takes place after prossingi-Z pieces.

'No'rs.Lubricant componentz-Steahic aeidzcyelohexylamine=80:20 in mol; Coupling agent:Dlethyleneglycol methyl" ether; Coating amount:0.8 g./m.'-.

It is clear from the results that, in pressing a steel sheet coated with a composition containing no coupling agent, the composition sticks enormously on the die, thus injuring the efiiciency of press work remarkably; and, on the contrary, when a composition containing a coupling agent in this invention is applied, no aging of the coating film takes place, and accordingly the press work can be carried out with a high efficiency.

EXAMPLE 3 The results of the experiment on the lubricity of a zinc plated cold rolled steel sheet with a thickness of 0.8 mm., coated with the composition of this invention (A), with a rust preventing oil (B) and with a press oil (C) were as shown in Table 4.

TABLE 4 Maximum Conical punch load Coated Erickson cup in cylindriamount, value, value, cal cup g./m. mm. mm. drawing, ton

Remarks: Composition of this invention:

stearic acid (82 mol)-70 wt. percent dicyclohexylamine (18 mol)-10 wt. percent diethyleneglycol methylether-20 wt. percent Rust preventing oil-viscosity SUS 60 seconds.

Press oil-viscosity SUS 120 seconds.

From the results of this experiment, it is clear that the composition of this invention exhibits an excellent lubricating ability as well for the zinc plated steel sheet. For the plated steel sheets, it is possible to diminish the content of amine as compared with the case for bare steel sheet.

What is claimed is:

1. A surface treated steel sheet for use in a forming operation having a coating layer of a composition which is a solid at ambient temperature, comprising 95-60 weight percent of a lubricant component consisting of -60 mol percent of a higher fatty acid having more than 10 carbon atoms, 10-40 mol percent of an amine selected from the group consisting of octylamine, cyclohexylamine, diisopropylamine, dicyclohexylamine, triethylamine, triethanolamine, oxazine, imidazol, and mixtures thereof, and 5-40 weight percent of a coupling agent consisting of a plasticizer having oxyethylene or oxypropylene radicals on the surface of the steel sheet.

2. Surface treated steel sheet according to claim 1 in which the amount of the coating on the steel sheet is in the range from 0.1-5 g./m.

3. Surface treated steel sheet according to claim 1, in which the higher fatty acid is stearic acid, palmitic acid or a mixture thereof.

4. Surface treated steel sheet according to claim 1, in which the amine is cyclohexylamine, dicyclohexyl amine or a mixture thereof.

References Cited UNITED STATES PATENTS 2,963,391 12/ 1960 Kubie 148-614 R 3,966,425 12/ 1960 Fucinari et al. 117-49 2,264,999 12/1941 Musselman 252-34 2,481,585 9/1949 Freeman 252-34 X 2,579,778 12/1951 Allen 117-134 X 2,741,567 4/1956 Otto 117-134 X 2,916,402 12/1959 Baird et a1 117-134 RALPH S. KENDALL, Primary Examiner U.S. C1. X.R. 

